Analysis: Polls show that 14 Senate seats are still up for grabs

With five days to go before Election Day, there are more close Senate contests than in any election in our three decades of covering congressional elections.

Fourteen of this year’s 33 Senate contests are within single digits, and a surge toward one party could tip the balance of power in the Senate.

If current polling holds up on Nov. 6, the Republicans would net one Senate seat, leaving Democrats with a slim majority (thanks to Independents who caucus with the Democrats).

Best-case scenario for Republicans: A gain of nine. And a Senate majority.

Best-case scenario for Democrats: A gain of two. And a bit of a cushion.

Here are the single-digit Senate contests, based on our analysis of RealClearPolitics data. Thanks to Max Kranl of the Hearst Washington bureau for collecting the numbers for us to slice and dice:

1. Montana: Denny Rehberg (R) vs. Sen. Jon Tester (D)

Average: Rehberg +0.3
Range: Rehberg +3 to Tester +2
Most recent polls: Rehberg leads one poll, Tester leads one, one a tie
Polling reliability: High
Rick Dunham’s analysis: Can Democrats turn out their voters in a red state to save their most endangered incumbent?

Average: Mourdock +1.3
Range: Mourdock +5 to Donnelly +2
Most recent polls: Mourdock leads in two polls, Donnelly in one, one a tie
Polling reliability: Moderate
Rick Dunham’s analysis: Internal polling showing a Mourdock dive after “rape” comment created a firestorm. But no recent public polling.

6. Nebraska: Deb Fischer (R) vs. Bob Kerrey (D)Average: Fischer +3
Range: None
Most recent polls: Fischer leads in the only public poll since September
Polling reliability: Low
Rick Dunham’s analysis: It’s a very Republican state, and there’s only one public poll. It’s not inconceivable that former Sen. Kerrey could pull an upset, but it’s highly unlikely with Romney running way ahead.

7. Nevada: Sen. Dean Heller (R) vs. Shelley Berkley (D)

Average: Heller +3.5
Range: Heller +6 to tie
Most recent polls: Heller leading in three of four polls, one a tie
Polling reliability: High
Rick Dunham’s analysis: Ethics issues have hurt Berkley in a state where Obama is slightly ahead.

8. Connecticut: Chris Murphy (D) vs. Linda McMahon (R)

Average: Murphy +4.0
Range: Murphy +6 to tie
Most recent polls: Murphy leading in three of four polls, one a tie
Polling reliability: High
Rick Dunham’s analysis: The polling trendline is with Murphy.

9. Massachusetts: Elizabeth Warren (D) vs. Sen. Scott Brown (R)

Average: Warren +4.5
Range: Warren +7 to tie
Most recent polls: Warren leading in three of four polls, one a tie
Polling reliability: High
Rick Dunham’s analysis: Barring a late shift, the Democratic challenger seems poised for a win.

10. Missouri: Sen. Claire McCaskill (D) vs. Todd Akin (R)

Average: McCaskill +5.0
Range: McCaskill +8 to McCaskill +2
Most recent polls: McCaskill leads in all four polls
Polling reliability: High
Rick Dunham’s analysis: McCaskill hasn’t been able to close the deal against a weak opponent.

11. Ohio: Sen. Sherrod Brown (D) vs. Josh Mandel (R)

Average: Brown +5.5
Range: Brown +11 to Brown +1
Most recent polls: Brown leads in all six polls
Polling reliability: Moderate
Rick Dunham’s analysis: The margin has varied widely, but Brown is ahead in every poll.

Average: Casey +6.2
Range: Casey +9 to Casey +1
Most recent polls: Casey leads in all four polls
Polling reliability: High
Rick Dunham’s analysis: Self-funding Republican has made this a real contest against a popular incumbent.

14. Florida: Sen. Bill Nelson (D) vs. Connie Mack (R)

Average: Nelson +6.7
Range: Nelson +13 to Nelson +3
Most recent polls: Nelson leads in all six polls
Polling reliability: High
Rick Dunham’s analysis: Mack needs a major Romney surge to pull even with the Democratic incumbent.